The present invention is related to the field of braking systems, and, more particularly, to railway braking systems and related methods.
Trains are widely used to transport people and freight. Freight trains in particular may be relatively long and include several groups of locomotives (consists). For example, a freight train may include 150 or more rail cars and extend over a mile or more. Coordination of control is required for operating the separated locomotives to ensure proper traction and braking, for example.
U.S. Pat. Nos. 4,582,280 and 4,553,723 to Nichols et al. are seminal patents directed to a radio communication based train control system. The radio communication system is for a lead unit and a plurality of remote units. The system includes a protocol for establishing a communication link between the lead unit and the one or more remote units. The protocol prevents any of the units in the system from processing messages or commands from other units in other train systems or processing messages or commands originating from units with the train system but which are addressed to other units. The control system provides for the coordinated control of the throttle and air braking functions in the train.
GE Harris Railway Electronics, L.L.C. offers a radio based control system under the designation LOCOTROL(copyright) which provides coordinated distributed power and air brake control of the remote locomotives from the lead locomotive as described in the above referenced patents. The system controls tractive effort and braking effort for up to four consists for all types of freight over all types of terrain. Each equipped unit can be operated as a head-end (lead unit), or a remote unit.
Distributed power and brake systems as described above which use radio communications for remote control and monitoring of unmanned locomotives also typically use the train brake pipe as a back-up communication link. This back-up link functions to idle the remote locomotives and cut-out control of the train brakes by the remote unit in the event of an interruption of the radio communications link. Without such a feature, a remote unit unable to receive radio communications could be operating adverse to the desired train operation. With the back-up link provided by the brake pipe, the train may continue to operate, such as to pass completely through a tunnel, for example.
Previous brake systems, such as the LOCOTROL(copyright) systems, have used pneumatic and electronic processing of the brake pipe charging flow rate at the remote unit to detect a brake application initiated by the driver at the lead unit. More particularly, the flow rate of air charging the brake pipe at the remote unit has been sensed by a differential pressure sensor associated with a restriction in a flow adaptor that is connected in fluid communication upstream of a relay valve. The relay valve selectively couples air from the main reservoir to charge the brake pipe at the remote unit. Alternately, the relay valve may also exhaust air from the brake pipe. The relay valve is controlled by a pressure in an equalizing reservoir which, in turn, is controlled under normal operations from electro-pneumatically operated valves controlled by the radio communication signals.
For example, if radio communications are lost and the lead unit causes an application of the brakes, a pressure reduction is propagated down the brake line. The flow sensor at the remote unit determines that the flow has increased indicative of brake application without receipt of the radio signal. This is used to cause the remote unit to cut-out its active braking control and idle the locomotive so that the remote unit becomes passive.
Unfortunately, the processing of the charging flow rate alone is become increasingly more difficult. This is so for two reasons. First, many railroads are operating remote locomotives from the end of the train. Accordingly, because of the increased effective length of the brake pipe through which the pneumatic signal must travel, flow sensing at the end of the train is more difficult than at a mid-train location, for example. Second, the characteristics of the typical relay valves used at remote units in some electronic brake systems differ from those used in the older style 26-L pneumatic systems. The 26-L relay valve typically begins to charge the brake pipe when the brake pipe is at a pressure less than 1 psi below the equalizing reservoir pressure. However, the relay valves used in electronic brake systems have been observed to delay charging the brake pipe until the pressure in the brake pipe is 2 psi or more below the equalizing reservoir pressure. This effect significantly desensitizes the air flow sensing approach as currently used, since the relay valve does not respond for the first 2 psi or more of pressure reduction in the brake pipe.
Another drawback with sensing only the flow rate is that some railroads may chose to operate a remote unit without the brake valve being operable. Accordingly, because the flow sensor is upstream of the relay valve, flow sensing alone cannot be used to detect the idle down command to the locomotive in the event of a loss of radio communications.
In view of the foregoing background, it is therefore an object of the present invention to provide a railway brake system which is more sensitive to the pneumatic control signal from a lead unit, but which also avoids false detections.
It is another object of the present invention to provide a railway brake system wherein a remote unit can receive an idle down signal from the brake pipe even when the flow sensing is not active.
These and other objects, features and advantages in accordance with the present invention are provided by a railway braking system comprising a brake pipe extending along the train, a lead unit controller generating a pneumatic control signal propagated along the brake pipe, and at least one remote unit controller. The remote unit controller preferably includes a brake pipe control valve, such as a relay valve, connected in fluid communication with the brake pipe for selectively charging and exhausting the brake pipe, and an air flow rate sensor for sensing air flow into the brake pipe during charging by the brake pipe control valve. More particularly, the remote unit controller also includes a brake pipe pressure sensor for sensing brake pipe pressure, and a processor for detecting the pneumatic control signal from the lead unit controller based upon both the air flow rate sensor and the brake pipe pressure sensor. Accordingly, the sensitivity of detection is increased despite delayed operation of a relay valve, for example, and while avoiding false indications.
The detection may be used to cut-out the remote unit controller and idle down the locomotive, as when radio communications are lost. The brake pressure sensing can also be used to receive a locomotive idle down command upon loss of radio communications and when the brake pipe control valve on the remote unit is not operating. The detection may also be used for brake pipe continuity testing and/or to determine the relative position of the remote unit relative to other remote units along the train.
The processor may comprise means for generating a sum of values representative of a change in air flow rate and a change in brake pipe pressure, and a comparator for comparing the sum of values to a threshold to detect the pneumatic control signal. In one embodiment, the air flow rate sensor comprises a restriction in fluid communication between the brake pipe and an air reservoir, and a differential pressure sensor associated with the restriction for sensing a differential pressure related to the air flow rate into the brake pipe. Accordingly, each value of the sum is based upon a change in differential pressure between a starting differential pressure and a respective sampled differential pressure, and a change in brake pipe pressure between a starting brake pipe pressure and a respective sampled brake pipe pressure multiplied by an effect multiplier. The effect multiplier takes into account the difference between the differential pressure sensing of the flow sensor, and the pressure sensing of the brake pipe pressure. The sum of values are preferably collected over a predetermined time.
According to another advantageous feature of the invention, the processor may have at least first and second sensitivities. For example, the first sensitivity may be lower for an initial brake application, and the second sensitivity may be greater for a supplemental brake application after the initial brake application. Accordingly, the dual sensitivities provide high accuracy of detection and while avoiding false detections. The two sensitivities may be obtained by using different times for collecting the flow and brake pressure data.
Of course, the brake control system preferably includes a radio communication system permitting remote control of the at least one remote unit controller by the lead unit controller by radio communication signals. Accordingly, the processor may further comprise cut-out means for cutting-out control of brake pipe pressure by the remote unit controller based upon a loss of radio communications and detecting the pneumatic control signal. The processor may also include locomotive idle down means for idling the locomotive, and based upon the pressure change alone as when the flow sensing is not active.
In accordance with another advantageous feature of the invention, the processor may further comprise continuity confirming means for confirming continuity of the brake pipe based upon a radio communication signal and detecting the pneumatic control signal, as when the train is first coupled together. In addition, the processor may include location determining means for determining a location of the at least one remote unit controller relative to other remote units based upon a radio communication signal and a time until detecting the pneumatic control signal.
A method aspect of the invention is for detecting receipt of a pneumatic control signal propagated along a brake pipe from a lead unit controller to at least one remote unit controller of a train brake system. The method preferably comprises the steps of using the remote unit controller for sensing air flow into the brake pipe during charging thereof, sensing brake pipe pressure, and detecting the pneumatic control signal from the lead unit controller based upon sensing of the air flow and brake pipe pressure.